Changing filename format based on current animation frame?
To make the output direct to specific directories dependent on frame you could add a handler to automatically set the scene.render.filepath before rendering the frame.

As an example, open a Text Editor window, click 'New' and enter the following code :


import bpy
def handler_set_filepath_based_on_frame(scene):
    scene.render.filepath = '//WalkingAnimation/%i_%i' % (scene.frame_current // 12, scene.frame_current % 12)
bpy.app.handlers.frame_change_pre.append(handler_set_filepath_based_on_frame)


Click the 'Run Script' button to run it and every time the frame changes the File Path should be automatically updated. Check the 'Register' checkbox to make it automatically run each time the .blend is opened.

If you then manually skip through the frames you should see the render output filepath automatically updating.

The calculation 'scene.frame_current // 12' is for the prefix and will increment by 1 for each 12 frames while the 'scene.frame_current % 12' will count the individual frame within each 12.